Using a non-invasive technique which measures respiration as a function of chest and abdominal movements, it was found that adult rats have periodic cessations in breathing analogous to human apneas. In preliminary studies in Fischer-344 rats apneas tended to be more frequent in 22-month-old than in 3-month-old rats. As in human apnea, apneas in Sprague-Dawley rats were significantly more frequent and longer in duration in REM sleep than in nonREM sleep or waking.